1. Field of the Invention
The present invention relates to a bioelectrical information acquisition device for obtaining bioelectrical information on a human body, such as electromyographic information or electrocardiographic information, through a plurality of electrodes attached to the human body. In particular, the present invention provides a bioelectrical information acquisition device and an inappropriately-attached-electrode identifying method which are capable of identifying, of a plurality of electrodes, an electrode which is inappropriately attached.
2. Description of the Related Art
In measuring bioelectrical information, such as, in electrocardiographic measurement or in electromyographic measurement, a biomedical electrode and a bio amp are generally used. The biomedical electrode is fixed onto skin with adhesive tape or the like, through which a feeble change in potential on the skin surface resulting from a heartbeat or from an action of the human body is detected, and the change is measured. In general, a feeble change in potential (several μV to several mV) derived by the electrode is amplified by the bio amp by several hundred to several thousand times, so as to be a signal that can be handled by common electronic equipment.
There exists an electric impedance between the biomedical electrode and the skin. The value of this electric impedance changes depending on how the electrode is attached to the skin (a contact state between the skin and the electrode). In measuring bioelectrical information, if the variation of the impedance is large, noise components (potential variations) resulting from the variation of the impedance are increased, with the result that a sufficient measurement accuracy (S/N ratio) cannot be obtained. In other words, in the case where an attachment state of the electrode (a contact state between the skin and the electrode) is not constant (in the case where an inappropriate attachment state is caused in the electrode), the bioelectrical information cannot be obtained with a sufficient measurement accuracy (S/N ratio). Further, if the electrode has peeled off, it is of course impossible to carry out the measurement.
Patent Document 1 mentioned below discloses a portable electrocardiographic monitor which allows a person to measure own electrocardiography. The portable electrocardiographic monitor according to Patent Document 1 includes a second measurement electrode disposed at a position which comes into contact with a hand of the person when the person holds the portable electrocardiographic monitor by hands, and a first measurement electrode is disposed on a main body part on which the second measurement electrode is provided. The first measurement electrode protrudes by a predetermined distance from the main body part which serves as a handle, and the person to be measured holds the main body part to press the first measurement electrode against the chest. According to the portable electrocardiographic monitor of Patent Document 1, the person to be measured holds by oneself the main body part (in a state where the hand is in contact with the second electrode), and presses the first electrode against the chest, whereby the potentials of the first electrode and the second electrode are measured. The portable electrocardiographic monitor of Patent Document 1 includes an impedance detecting circuit for detecting an impedance between the electrodes. In a case where the electrodes are not in complete contact with the skin of the person to be measured, that is, an inappropriate impedance is detected, a warning operation is performed by an LED or a warning sound is generated by a buzzer, to thereby notify the person to be measured that the contact of the electrodes is inappropriate. In other words, it is possible to detect an inappropriate impedance resulting from a poor contact of the electrodes, and when the inappropriate impedance (an inappropriate contact of the electrode) is detected, it is judged that the measurement operation is failure and a warning is generated.